NATO says a bomb blast has killed four of its service members in Afghanistan.

The international coalition say the foreign troops were killed Saturday in the eastern region of the country.

Earlier in the day, NATO said two of its members were killed Friday in separate attacks in southern Afghanistan.

At least 220 foreign troops have been killed in Afghanistan this year.

The U.S. commander of foreign troops in Afghanistan, General David Petraeus, warned last month of a tough summer ahead as insurgents bid to show they are still a potent force amid what he said was crucial progress made by the international coalition.

The Taliban announced the start of its spring and summer fighting season at the end of April.